Investigation of the effects of welding parameters on the weld strength in friction stir welding of high density polyethylene polymer material and optimization of welding parameters with taguchi experimental design method

In this thesis, the effect of important process and tool parameters on joint strength in friction stir welding of high density polyethylene plates has been investigated by using Taguchi experimental design method.The tool rotation, feed rate, tool shoulder diameter were considered as varying parameter and optimized with considerations of joint strength. Three different tool rotations, feed rates with shoulder geometries were used to fabricate the joints. The quality of the joint was evaluated by examining the characteristics of the joint efficiency as a result of ultimate tensile strength. The Taguchi approach of parameter design was used as a statistical design of experiment technique to set the optimal welding parameters. For friction stir welding of the plates, the experiments were arranged by using Taguchi's L9 orthogonal array in randomized way. The signal to noise ratio and the analysis of variance are employed to investigate friction stir welding parameter effects on the joint strength. From the analysis of variance and the signal to noise response graphs, the significant parameters and the optimal combination level of welding parameters were obtained. It was found that using 1600 rpm of tool rotation, 20 mm/min of feed rate and 20 mm of shoulder diameter, it may be achieved improved joint strength.The results showed that feed rate, shoulder diameter and tool rotation were significant factors respectively. A confirmation run is also performed to prove the effectiveness of Taguchi method after the optimum levels of process parameters are determined. The weld strength was improved by about 25% from initial welding parameters. Consequently, a remarkable improvement was observed in joint efficiency as increase from 57% to 71%.